Reliability scheme using hybrid SSD/HDD replication with log structured management

ABSTRACT

In one embodiment, a method of managing data includes storing a first copy of data in a solid state memory using a controller of the solid state memory, and storing a second copy of the data in a hard disk drive memory using the controller. Write requests are served substantially simultaneously at both the solid state memory and the hard disk drive memory under control of the controller. In another embodiment, a system for storing data includes a solid state memory, at least one hard disk drive memory, and a controller for controlling storage of data in both the solid state memory and the hard disk drive memory. Other methods, systems, and computer program products are also described according to various embodiments.

BACKGROUND

Information-handling systems may have different types of permanentstorage devices. One information-handling system has a processor capableof processing information and of generating a storage task, a hard diskdrive interface with a processor, the hard disk drive being capable ofstoring information on a rotating magnetic disk and of performing astorage task, a solid state drive interface with the processor, thesolid state drive being capable of storing information in flash memoryand of performing the storage task, and a storage arbitrator interfacewith a hard disk drive and the solid state drive, the storage arbitratorbeing capable of selecting one of the hard disk drives with a solidstate drive to perform a predetermined task based on one or morefactors. Furthermore, the information-handling system has a redundantarray of independent disks (RAID) controller interfaced with a hard diskdrive and a solid state drive. The RAID controller is capable ofmirroring information stored on the hard disk drive and the solid statedrive.

SUMMARY

In one embodiment, a computer-implemented method of managing dataincludes storing a first copy of data in a solid state memory using acontroller of the solid state memory and storing a second copy of thedata in a hard disk drive memory using the controller. Write requestsare served substantially simultaneously at both the solid state memoryand the hard disk drive memory under control of the controller.

In another embodiment, a system for storing data includes a solid statememory, at least one hard disk drive memory, and a controller forcontrolling storage of data in both the solid state memory and the harddisk drive memory. The controller is configured to cause erasure of thefirst copy of the data from the solid state memory in response toreceiving the request to erase the data. However, the second copy of thedata is not also immediately erased from the hard disk drive memory.

In another embodiment, a computer program product for storing data on adata storage system includes a computer readable storage medium havingprogram instructions embodied therewith. The computer readable storagemedium is not a transitory signal per se. The program instructions areexecutable by a controller to cause the controller to perform a methodincluding managing, by the controller, a first copy of data in a solidstate memory; managing, by the controller, a second copy of the data ina hard disk drive memory using the controller; receiving, by thecontroller, a request to erase the data; and causing, by the controller,erasing of the first copy of the data from the solid state memory inresponse to receiving the request to erase the data, wherein the secondcopy of the data is not also immediately erased from the hard disk drivememory.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a first embodiment of a data storage system.

FIG. 2 depicts a second embodiment of a data storage system.

FIG. 3 depicts a third embodiment of a data storage system.

FIG. 4 depicts a flow chart of a writing process, according to oneembodiment.

FIG. 5 depicts a computer program product, according to one embodiment.

FIG. 6 depicts a flow chart of a method for storing infrequently useddata on a hard disk drive, in one embodiment.

FIG. 7 depicts a first map, according to one embodiment.

FIG. 8 depicts another map, according to one embodiment.

FIG. 9 shows a flowchart of a method, according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

In one general embodiment, a method of storing data includes storing afirst copy of data in a solid state memory and storing a second copy ofthe data in a hard disk drive memory substantially simultaneously withthe storing the first copy.

In another general embodiment, a system for storing data includes asolid state memory, at least one hard disk drive memory, and acontroller for controlling storage of data in the solid state memory andthe hard disk drive memory, wherein a first copy of the data is storedin the solid state memory substantially simultaneously with storing asecond copy of the data in the at least one hard disk drive memory.

In another general embodiment, a computer program product for storingdata on a data storage system includes a computer readable storagemedium having computer readable program code embodied therewith. Thecomputer readable program code includes computer readable program codeconfigured to store a first copy of data in a solid state memory, andcomputer readable program code configured to store a second copy of thedata in a hard disk drive memory substantially simultaneously with thestoring the first copy.

In one embodiment, a method of storing data using a solid state memoryand a hard disk drive (HDD) uses a controller which controls the storingof the data in the solid state memory and in the HDD. The method iscapable of providing a cost-effective yet high-performingreplication-based reliability scheme for solid state memory, e.g., flashmemory.

In another embodiment, a system uses one or more HDDs to store areplicated copy for data stored on the solid state memory. Thereplicated data on the HDD is managed by the same controller thatcontrols data on the solid state memory. In a further embodiment, dataon the HDD are managed in the same way as data on the solid statememory.

According to another embodiment, all read-requests are served by solidstate memory and all write-requests are served by either of the solidstate memory and/or the HDD. In a further embodiment, the write requestsare served by the solid state memory and the HDD, simultaneously.

In some approaches, physical blocks of solid state memory may bevirtually associated with logical or physical segments of the HDD. Inthis way, the proposed system is cost-effective and provides a highdata-throughput.

Another embodiment refers to a method of storing data, whereby the datais written simultaneously to the solid state memory and the HDD, orfirst to the solid state memory and then to the HDD. This methodprovides for fast storing of the data by replicating the data using HDD.

In another approach, a block of the solid state memory is accessed andthe same data is written in an associated corresponding disk segment ofHDD.

Another embodiment includes a method of storing data, wherein the methodrefers to reading data only from the solid state memory and not from theHDD. The HDD may only be arranged for providing a security-backup of thedata. If the data of the solid state memory are defective or the solidstate memory becomes broken, the data can be read from the HDD.

In another approach, storing data refers to erasing data only on thesolid state memory, because it is not necessary to erase data beforewriting new data onto the HDD. As a result, the operating of the systemis simplified.

In one embodiment, a cost-effective yet high-performingreplication-based reliability method for solid state drives (SSDs),e.g., flash drives, uses one or more HDDs to store the replicated datapages stored on the solid state memory. The replicated data on theHDD(s) is managed, by the flash controller, in exactly the same way asdata pages on the solid state memory. All read requests may be served byflash memory, and write requests may be served simultaneously at boththe solid state memory and the HDDs in an append mode controlled by thesolid state controller. This may be accomplished by virtuallyassociating each physical solid state block with a physical chunk ofdisk space, which may be addressed by logical block addressing (LBA),and may use the solid state controller to manage data copies on both thesolid state memory and the HDD. The advantages of this scheme arecost-effectiveness and higher throughput.

FIG. 1 depicts a schematic diagram of a first embodiment of a storagesystem 100 with a controller 1 that comprises a memory 2 and a processor3. The memory may be solid state memory, such as flash, RAM, DRAM, etc.,or any other fast access memory. The processor 3 may be a processor, afield programmable gate array (FPGA), an application specific integratedcircuit (ASIC), etc. The controller 1 is coupled via an interface 4 witha solid state drive (SSD) 5 and hard disk drive (HDD) 6, both the SSDand HDD acting as computer readable memory. The SSD 5 may, for example,be embodied as a flash-type memory. In this case, the controller 1 isembodied as a flash-controller. The connection 4 may be embodied asconnecting lines or a data bus that connects the controller 1 with theSSD 5 and HDD 6. The connection 4 to the SSD 5 and the HDD 6 may bebased on different technologies. In this case, the connection 4 to theSSD 5 and the HDD 6 are separated. In the memory 2, programs are storedthat are used by the processor to perform the function of the controller1. The controller 1 comprises an input/output (I/O) 30 for exchangingdata and control signals with a host computer. The HDD may comprise, asan example, a memory disk, a controller, and a buffer memory. Data andcontrol signals are exchanged by an I/O interface. The details are notshown in the figure.

The SSD 5 is organized in data blocks which are used for storing data.For example, a solid state-memory page, such as a flash-memory page, mayhave a size of 4 KB and a solid state-memory block, such as aflash-memory block, may be made of 64 flash pages. Reading and writingoperations may be performed on a page-basis while erasing operations areperformed per block. This means that one reading operation always readsthe data of a whole page. Also, during one writing operation the data ofa whole page are always written. During one erasing operation, a wholeblock of data, comprising 64 memory-pages is always erased. Sinceerasing a block of data takes much longer than a page-read or apage-write, out-of-place writes are commonly used in solid state-memoryto improve the write performance and to mitigate an even wear-out.

The HDD 6 may be organized into data segments 8. For each data block 7of the SSD 5, a corresponding data segment 8, preferably of the samesize, e.g., 256 KB, may be arranged. Furthermore, the data is stored inthe same way in the data block 7 and in the data segment 8. The reading,writing, and erasing of data is performed by the controller 1, whichpossibly resides separately or together with the solid state-memory, andare performed, for example, in an appended mode. For example, a virtualassociation of each physical block 7 of the solid state-memory with aphysical data segment 8 of the HDD may be used. For example, the datamay be addressed by the method logical block addressing (LBA) and thecontroller 1 may be used to manage data copies on both the SSD and HDD.This means that each data is written in the SSD 5 and in the HDD 6. Forexample, each data segment 8 of the HDD is mapped to a data block 7 ofthe SSD 5. Therefore, the system and the method are cost-effective andprovide a high throughput.

In order to perform out-of-place writes, the controller implements a setof functions such as host LA (logical address) to PA (physical solidstate-address) mapping, such as flash translation layer FTL,garbage-collection, wear-labeling, and bad-block management which aresimilar to functions performed in a log-structured file system.

In one embodiment, the controller 1 always writes data sequentially oneach free block on the SSD and at the same time, the controller issuesdisk write commands to the HDD and sends the same data to the HDD towrite the data to the HDD. The controller maintains host LA-PA mappingin the memory 2 and a check point of host LA-PA map on both SSD and HDDusing a dedicated area, for failure recovery reasons. Both SSD and HDDare used as multiple small block-sized logs, each having a size of 256KB in case of a solid state block consisting of 64*4 KB pages, andappend new data to the end of the log, while old data is invalidated.Note that the size of each block can be one solid state-block ormultiple solid state-blocks. The controller may use garbage collectionto identify suitable solid state-blocks to be relocated and erased.After all valid data blocks on the erase block have been written to anew location, the block may be erased and may be used as a free block toaccommodate new writes. One approach is that every solid state-blockwhich has a typical size of 256 KB is associated with one (or more) datasegments of the disk LBA space, so that data on that solid state-blockis replicated on its associated disk segment of the HDD. If a solidstate-data page is moved, during garbage collection, from one solidstate-block to another, it may also be written to a new correspondinglocation, e.g., to a corresponding new disk segment on the HDD.

Consequently, both SSD and HDD rely on the same controlling functions inthe controller 1 to perform out-of-place writes and log-structuredmanagement, sharing the same host LA-PA map (e.g., FTL) and garbagecollection functions. The benefit of doing out-of-place writes even onHDD is that a random write workload may be transformed into a sequentialwrite one, which can accelerate disk write speed to match the speed ofthe SSD. In other words, disks are therefore mostly used in sequentialmode to append write data, sustaining their peak transfer rates withminimal positioning overhead and potentially matching the highthroughput of SSDs.

A write request is considered finished only if the data has been writtensuccessfully to both SSD and HDD. For all read-requests, the controllermay read the data only from the SSD 5. In case of a failure of the SSD5, the controller 1 will get the data from the HDD as there is always acopy of the data of the SSD on the HDD. In the case that the HDD fails,the controller will replicate data from SSD to another HDD. In case of acontroller failure, another controller which performs the same functionsmay take over the control. This controller fail-over requires that allmetadata used by the controller be stored safely (e.g., via check-pointand logging) on both the SSD and HDD(s), so that the system can recovereven from a controller failure.

In the embodiment shown in FIG. 1, the SSD 5 may have the same amount ofstorage space as one HDD 6. In a further embodiment, the SSD 5 uses lessstorage space than one HDD 6. The idea is to store both copies of datathat are being accessed infrequently on the HDD only (preferably twocopies on two different HDDs for reliability reasons) instead of onecopy on the SSD and one copy on the HDD.

As a specific example, it is assumed that a SSD 5 has a storage space of256 GB and a HDD has a storage page 512 GB. So, two SSDs and three HDDscould be used in a configuration that supports 1 TB of capacity asfollows: each SSD has its own corresponding HDD. The third HDD is usedfor data being moved out of a SSD when garbage collection runs. Data onthe third HDD is, therefore, data that is not frequently accessed, sothere is still good overall performance for read/write requests. Theabove configuration may be further improved by splitting each HDD intotwo virtual sub-HDDs having ⅙ of the total HDD capacity, anddistributing these chunks evenly over all HDDs, with the aim toguarantee that the two copies of infrequently accessed data is stored ondifferent HDDs. Analogously, the splitting is not limited to thisexample, but may be done in a similar way with a similar aim for any HDDconfiguration.

The schemes disclosed herein that make use of a SSD, for example a flashmemory, as a main memory for accessing data, and HDDs for replication,may be naturally extended. For instance, a controller together with aSSD may be used to serve read and write requests, and the same writesmay also be served by a redundant array of independent disks (RAID)controller connected with multiple HDDs for data preservation reasons.The data stored on the HDDs will only be accessed for data recovery inthis approach. The RAID controller may or may not use a log-structuredmanagement scheme to manage the replicated data on the HDDs. Thecontroller might be arranged on the same card with solid state memory,but is not limited to that arrangement. In other words, the controllermay also be a stand-alone module that may control data storage to themultiple HDDs and the SSD, in one approach.

FIG. 2 shows a second embodiment of the storage system 200 thatcomprises a controller 1 with a memory 2 and a processor 3. The memory 2and processor 3 may be of any type known in the art, as describedpreviously. The controller 1 is coupled with a SSD memory 5 via aconnection 4 and a first, second, and a third HDD memory 6, 9, 10. Inthis embodiment, three HDD storage devices are used, but any numbergreater than one may be used, in this or any other embodiment. The datablocks 7, 11, 13, of the SSD 5 are associated with data segments 8, 12,14 of different HDDs 6, 9, 10. For example, the first data block 7 ofthe SSD 5 is associated with a first data segment 8 of the first HDD 6.The second data block 11 of the SSD 5 is associated with a second datasegment 12 of the second HDD 9. A third data block 13 of the SSD 5 isassociated with a third data segment 14 of the third HDD 10. This meansthat the data that are written in the different data blocks 7, 11, 13 ofthe SSD 5 are duplicated in several HDDs 6, 9, 10. Of course, the SSDmay be any type of device that uses solid state memory, such as flashmemory, in various embodiments.

FIG. 3 shows a third embodiment of a storage system 300. This embodimentcomprises the controller 1 with memory 2 and a processor 3. The memory 2and processor 3 may be of any type known in the art, as previouslydescribed. Furthermore, the controller 1 is coupled with the SSD memory5 via a connection 4 and a disk system 15. The disk system 15 comprisesa second controller 16. The second controller 16 is embodied as a RAIDcontroller that controls the data exchange between the controller 1 andseveral further HDDs 17, 18, 19. Again, in this embodiment, three HDDsare used, but any number greater than one may be used in this or anyother embodiment.

In this embodiment, the data blocks 7, 11, 13 of the SSD 5 areassociated with data segments 20, 21, 22 of at least one of the HDDs 17,18, 19, and as shown in FIG. 3, they are spread across all three HDDs17, 18, 19. The handling of the data for storing the data in the HDDs17, 18, 19 is handed over from the controller 1 to the second controller16.

FIG. 4 shows a schematic flow chart of a method 400 for storing data ina data storage system, for example, according to the embodiment ofFIG. 1. For example, the controller 1 may receive via an input/output(I/O) 30 that is connected with memory 2 and a processor 3, a requestfrom a host computer to store data which is depicted, as shown in FIG.4, in operation 50, according to one embodiment. Referring to FIGS. 1and 4, the host computer delivers the data and a logical address for thedata. In operation 55, the controller 1 searches for a free page of adata block 7 of the flash memory 5, according to one embodiment. Inoperation 60, the controller writes the data into the selected page ofthe flash memory 5 and updates metadata, according to one embodiment.

The logical address from the host computer is stored in the memory 2. Alogical address of the flash controller for the stored data is alsostored in the memory. A physical address of the selected page at whichthe data is stored is also stored in the memory. Metadata is a sort ofcontrol information which may be stored in the memory 2, the SSD 5, andin the HDD 6. The metadata is essential for deciding on the rightpolicies and activities to the access to the flash memory. A simpleexample is the storing of the erase count of each of the blocks in thestorage systems. As there is a desire to level out the usage of blocksacross the storage system as blocks wear out with extended use, it istypical for a solid state memory system to maintain for each block anumber of accumulated erase cycles and use these data for deciding onthe next block to be allocated for writing new incoming data. Many ofthe metadata types commonly used are block-specific. The metadataprovide some information that is a characteristic of the block as awhole. Furthermore, there may also be metadata types that arepage-specific which means that they provide information related only toa specific page, and different pages within the same block may havedifferent metadata values. One common example for page-specific metadatais the error-correction parity bit typically stored on each page of userdata to enable error correction when reading the page. In case of powerfailures, the metadata may be stored to a SSD region dedicated formetadata, according to one embodiment.

In operation 65, the same data that were written into the flash memory 5are now written into the HDD 6. A logical address of the segment of theHDD and the data is delivered from the controller 1 to the HDD 6. Thecontroller stores a map that determines the assignment of the datablocks of the SSD 5 to determined disk segments of the HDD 6 in thememory 2. The data is, for example, written into a page of the HDDsegment mirroring the solid state-block in which the same data werewritten before. For example, the addressing on the HDD 6 may beperformed by using conventional logical block-addressing (LBA). Thecontroller keeps a map table in the memory 2, according to oneembodiment, from physical flash block address to disk logical blockaddress, to record the association between a physical solid state-blockand its disk copy on a HDD. The controller also implements a LA-PAmapping, such as flash translation layer (FTL), to keep track of themappings of host logical address to solid state-physical address,enabling write-out-of-place. With the help of LA-PA mapping, incomingwrite requests may be served sequentially on individual solidstate-blocks, therefore the writing on disks is sequential within HDDsegments due to the one-to-one correspondence between a solidstate-block and a HDD segment.

In operation 70, which is not necessary nor required in all cases, thecontroller checks if the total number of free solid state-pages of theSSD 5 is below a threshold. If this is the case, then thegarbage-collection program is triggered on the SSD 5. Then theprocessing is stopped at operation 75.

If there is an embodiment as depicted in FIG. 3 with a disk system 15comprising a second controller 16 that controls several HDDs 17, 18, 19,then the controller 3 delivers the data and the logical address of thedata that have to be stored in the HDDs to the second controller 16.This means that, referring to the method depicted in FIG. 4, the writingof data in the HDDs in operation 65 is performed by the secondcontroller 16.

The flow chart depicted in FIG. 4 is just one example of manyembodiments possible using the techniques and systems described hereinaccording to various embodiments. There may be many variations to thisflow chart or the operations described therein without departing fromthe spirit and scope of the invention. For instance, the operations maybe performed in a different order or operations may be added, deleted,or modified, or certain operations may be executed in parallel if thestructure of the system allows for this. All of these variations areconsidered a part of the present invention.

The one-to-one map between SSD and HDD segment described above is basedon the size of a single solid state-block. The map may naturally be donebased on multiple solid state-blocks, meaning that one disk segment maybe associated with a set of solid state-blocks, may be of the same size,and that data may be sequentially written to the set of solidstate-blocks and the corresponding disk segment, respectively.

FIG. 5 depicts a computer program product 80, for example embodied as amemory circuit, a DVD-ROM, a CD-ROM, a BD-ROM, etc., that is embodied ina computer-readable medium for causing a computer to control a methodfor storing data, as described above.

It will be clear that the various features of the foregoingmethodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will also be clear to one skilled in the art that the methodology ofthe present invention may suitably be embodied in a logic apparatuscomprising logic to perform various steps of the methodology presentedherein, and that such logic may comprise hardware components or firmwarecomponents.

It will be equally clear to one skilled in the art that the logicarrangement in various approaches may suitably be embodied in a logicapparatus comprising logic to perform various steps of the method, andthat such logic may comprise components such as logic gates in, forexample, a programmable logic array. Such a logic arrangement mayfurther be embodied in enabling means or components for temporarily orpermanently establishing logical structures in such an array using, forexample, a virtual hardware descriptor language, which may be storedusing fixed or transmittable carrier media.

It will be appreciated that the methodology described above may alsosuitably be carried out fully or partially in software running on one ormore processors (not shown), and that the software may be provided as acomputer program element carried on any suitable data carrier (also notshown) such as a magnetic or optical computer disk. The channels for thetransmission of data likewise may include storage media of alldescriptions as well as signal carrying media, such as wired or wirelesssignal media.

Embodiments of the present invention may suitably be embodied as acomputer program product for use with a computer system. Such animplementation may comprise a series of computer readable instructionseither fixed on a non-transitory medium, such as a computer readablemedium, for example, diskette, CD-ROM, DVD-ROM, BD-ROM, ROM, hard disk,etc., or transmittable to a computer system, via a modem or otherinterface device, over either a tangible medium, including but notlimited to optical or analogue communications lines, or intangibly usingwireless techniques, including but not limited to microwave, infrared orother transmission techniques. The series of computer readableinstructions embodies all or part of the functionality previouslydescribed herein.

Those skilled in the art will appreciate that such computer readableinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Further, suchinstructions may be stored using any memory technology, present orfuture, including but not limited to, semiconductor, magnetic, oroptical, or transmitted using any communications technology, present orfuture, including but not limited to optical, infrared, or microwave. Itis contemplated that such a computer program product may be distributedas a removable medium with accompanying printed or electronicdocumentation, for example, shrink-wrapped software, pre-loaded with acomputer system, for example, on a system ROM or fixed disk, ordistributed from a server or electronic bulletin board over a network,for example, the Internet or World Wide Web.

Communications components such as input/output or I/O devices (includingbut not limited to keyboards, displays, pointing devices, etc.) can becoupled to the system either directly or through intervening I/Ocontrollers.

Communications components such as buses, interfaces, network adapters,etc. may also be coupled to the system to enable the data processingsystem, e.g., host, to become coupled to other data processing systemsor remote printers or storage devices through intervening private orpublic networks. Modems, cable modem and Ethernet cards are just a fewof the currently available types of network adapters.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer to offer service on demand.

FIG. 6 shows a flow chart of a method 600 for storing data that are notfrequently used, according to one embodiment. This method may be usedfor data read from the SSD and then stored to the HDD with a storagesystem as shown in FIG. 1, for example. The description of the method inFIG. 6 will now be made with reference to FIG. 1.

In operation 85, the controller 1 checks the SSD 5 for data that areused infrequently, which typically means that the data is infrequentlyread, but may also include data that were not recently written,regardless of last read. The controller may use a reference value fordeciding which data is used frequently and which not. At operation 90,the controller 1 stores the infrequently used data of the SSD 5 to theHDD 6.

In operation 95, the controller 1 deletes the infrequently used data inthe SSD 5. As a result, the infrequently used data is stored twice onthe HDD 6 because the data were stored once on the HDD 6 when they werestored on the SSD 5 originally.

FIG. 7 depicts a map 700 that may be used by a processor and thatassigns a logical address of data that is received by the host computerto a logical address of data on a SSD. Furthermore, the logical addressof the data on the SSD is assigned to a physical address of the SSD. Themap is stored and updated on the memory of the system.

FIG. 8 depicts another map 800 that may be used by a processorcontrolling the storage of the data on a HDD. This map 800 shows theassignment of a physical address of data stored in a SSD and the logicaladdress at which the same data is stored on the HDD. The physicaladdress of the SSD may be a block address and/or a page address. Thelogical address of the HDD may be a physical disk segment address of thedisk of the HDD. The map 800 may be stored and updated on the memory ofthe system.

Now referring to FIG. 9, a method 900 for storing data is shownaccording to one embodiment. The method 900 may be carried out in anydesired environment, including those shown in FIGS. 1-8, among others,according to various embodiments.

In operation 905, a first copy of data is stored in a solid statememory. The solid state memory may be of any type known in the art, suchas those described herein, among others, according to variousembodiments.

In operation 910, a second copy of the data is stored in a hard diskdrive memory, substantially simultaneously with the storing the firstcopy. Since solid state memory generally is capable of faster accesstimes, even if operations 905 and 910 are performed simultaneously, thefirst copy typically will be written first, followed by the second copy,but the method 900 is not so limited. In some cases, the solid statememory may be busy or in some other way incapable of being accessed, inwhich case the second copy may be completely written to the HDD memorybefore the first copy is completely written to the solid state memory.Regardless, the storing operations in these cases are all considered tobe “substantially simultaneously.”

In one embodiment, a map may be used to store the data. The map may showa correlation between a physical solid state memory block address on thesolid state memory and an assigned logical disk block address on the HDDmemory that have the same data stored therein. In a further approach, atranslation layer may be used to keep track of mappings of host logicaladdresses to solid state memory physical addresses.

According to one embodiment, storing the data may include writing thedata in a solid state memory block and a disk segment of the HDD memoryand associating the disk segment of the HDD memory with the solid statememory block. This association may be stored to the map, as previouslydescribed, or may be stored using any other technique known in the artsuch that it may be referenced to determine the association between thedata stored in the solid state memory and the HDD memory.

In one embodiment, the method 900 may further include receiving arequest to read the data and in response to receiving the request toread the data, the first copy of the data from the solid state memorymay be read unless there is a failure of the solid state memory, inwhich case the second copy of the data may be read from the HDD memory.

According to yet another embodiment, the method 900 may further includereceiving a request to erase the data and in response to receiving therequest to erase the data, the first copy of the data may be erased fromthe solid state memory, with the proviso that the second copy of thedata is not also erased from the HDD memory substantially concurrentlywith the erasure of the data from the solid state memory. Rather, thesecond copy may remain in the HDD memory until a request to erase thesecond copy is received, the second copy expires, after a predeterminedtime elapses, the storage location of the second copy is needed forother data, etc.

In one approach, the solid state memory and the HDD memory may becontrolled by a controller of the solid state memory. In an alternateembodiment, the solid state memory and the HDD memory may be controlledby a controller of the HDD memory.

In a further embodiment, the controller may use a map to store the data.The map may be as previously described, or any other method as known inthe art may be used to store the correlation between a physical solidstate memory block address on the solid state memory and an assignedlogical disk block address on the hard disk drive memory that have thesame data stored therein.

In one embodiment, a system may include a solid state memory, at leastone HDD memory, and a controller for controlling storage of data in thesolid state memory and the HDD memory. In one approach, during normaloperation of the system, reading operations may only be performed on thesolid state memory, except during a failure of the solid state memory,when reading operations may be performed on the HDD memory.

In one approach, the system may include at least one more hard diskdrive memory. In this approach, the controller may be a RAID controllerthat controls storage of data in the solid state memory and in all HDDmemories, but is not so limited.

In one embodiment, less frequently accessed data may be stored on afirst and a second hard disk drive memory, with the proviso that lessfrequently accessed data is not stored on the solid state memory. In afurther embodiment, a garbage collection process may be used todetermine whether data is frequently accessed or not.

According to one embodiment, a computer program product for storing dataon a data storage system may include a computer readable storage mediumhaving computer readable program code embodied therewith. The computerreadable program code may have any of the functionality describedherein, according to various embodiments.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A computer program product for managing data on a storage system, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, wherein the computer readable storage medium is not a transitory signal per se, the program instructions executable by a controller to cause the controller to perform a method comprising: managing, by the controller, a first copy of data in a solid state memory; managing, by the controller, a second copy of the data in a hard disk drive memory using the controller; receiving, by the controller, a request to erase the data; and causing, by the controller, erasing of the first copy of the data from the solid state memory in response to receiving the request to erase the data, wherein the second copy of the data is not also immediately erased from the hard disk drive memory.
 2. The computer program product as recited in claim 1, wherein the second copy of the data is managed by the controller in a same way as the first copy is managed by the controller.
 3. The computer program product as recited in claim 1, wherein read requests are served by the solid state memory.
 4. The computer program product as recited in claim 1, wherein write requests are served substantially simultaneously at both the solid state memory and the hard disk drive memory under control of the controller.
 5. The computer program product as recited in claim 4, comprising program instructions executable by the controller to cause the controller to virtually associate each physical solid state block with a physical chunk of disk space.
 6. The computer program product as recited in claim 4, wherein the write requests are served at the hard disk drive memory in an append mode controlled by the controller.
 7. The computer program product as recited in claim 1, comprising program instructions executable by the controller to cause the controller to serve a read request for the data from the hard disk drive memory when the solid state memory fails.
 8. The computer program product as recited in claim 1, comprising program instructions executable by the controller to cause the controller to replicate the data from the solid state memory to a second hard disk drive memory when the hard disk drive memory fails.
 9. The computer program product as recited in claim 1, comprising program instructions executable by a second controller to cause the second controller to manage the copies of the data when the controller fails, the second controller using metadata stored on the solid state memory and the hard disk drive memory when taking over control.
 10. The computer program product as recited in claim 1, wherein the controller uses a map to store the data, wherein the map shows a correlation between a physical solid state memory block address on the solid state memory and an assigned logical disk block address on the hard disk drive memory that have the data stored therein, and wherein the controller uses a translation layer to keep track of mappings of host logical addresses to solid state memory physical addresses.
 11. A system for storing data, the system comprising: a solid state memory; at least one hard disk drive memory; and a controller for controlling storage of data in both the solid state memory and the hard disk drive memory, the controller being configured to cause erasure of a first copy of the data from the solid state memory in response to receiving a request to erase the data, wherein a second copy of the data is not also immediately erased from the hard disk drive memory.
 12. The system as recited in claim 11, wherein the solid state memory comprises memory blocks, wherein the hard disk drive memory comprises disk segments, wherein a memory block of the solid state memory is assigned to a disk segment of the hard disk drive memory, and wherein data that is written in the memory block of the solid state memory is also written in the assigned disk segment of the hard disk drive memory.
 13. The system as recited in claim 11, wherein during normal operation of the system, reading operations are only performed on the solid state memory, and wherein during a failure of the solid state memory, reading operations are performed on the hard disk drive memory.
 14. The system as recited in claim 11, comprising at least one more hard disk drive memory, wherein the controller is a redundant array of independent disks (RAID) controller that controls storage of data in the solid state memory and in all hard disk drive memories.
 15. The system as recited in claim 11, wherein less frequently accessed data is stored on a first and a second hard disk drive memory, with the proviso that less frequently accessed data is not stored on the solid state memory.
 16. The system as recited in claim 11, wherein the controller uses a map to store data on the solid state memory and the hard disk drive memory, wherein the map shows a correlation between a physical solid state memory block address on the solid state memory and an assigned logical disk block address on the hard disk drive memory that have the same data stored therein, wherein the controller uses a translation layer to keep track of mappings of host logical addresses to solid state memory physical addresses.
 17. A computer-implemented method, comprising: storing a first copy of data in a solid state memory using a controller of the solid state memory; and storing a second copy of the data in a hard disk drive memory using the controller of the solid state memory; and storing metadata in both the solid state memory and the hard disk drive memory for enabling a second controller to manage the copies of the data in response to failure of the controller, wherein write requests are served substantially simultaneously at both the solid state memory and the hard disk drive memory under control of the controller, wherein the write requests are served at the hard disk drive memory in an append mode controlled by the controller.
 18. The method as recited in claim 17, comprising reading the first copy of data from the solid state memory unless there is a failure of the solid state memory, in which case the second copy of the data is read from the hard disk drive memory. 